This invention relates generally to thread rolling dies and the manner in which the dies are formed. More specifically, this invention relates to thread rolling dies which are used to form lock teeth on the flank of an external thread convolution.
Dies have previously been used to roll designs in various types of articles and to roll external thread convolutions having lock teeth or retainer elements. The dies which are used to roll thread convolutions have thread form ridges or ribs with flanks having indentations which are used to roll the lock teeth on the flank of an external thread convolution. Dies for rolling such a thread convolution are disclosed in U.S. Pat. Nos. 4,136,416 and 3,339,389.
Although dies have previously been used to roll external thread convolutions having lock teeth, difficulty has been encountered in making the dies with projections and/or indentations which will form curved locking teeth of a specific desired arcuate configuration on the flank of the external thread convolution. This difficulty has resulted from the transferring of projections and/or indentations formed on a die with a linear motion of a tool to a thread convolution with a rolling motion. The difference between the linear motion used to form the die and the rolling motion used to form the thread distorts the shape of the projections and/or indentations.
It has been suggested that a blade or tool could be pressed against the flank of a thread form ridge of a die to form the projections and/or indentations in the flank of the thread form ridge, for example, see U.S. Pat. No. 3,653,241. However, the use of a blade or tool to stamp projections and/or indentations in the flank of a thread form ridge of a die is difficult since the blade tends to trap material which opposes the forming of the projections and/or indentations. In addition, it is difficult to determine the extent to which the blade is indented into the thread form ridge of the die. This is because a relatively large force must be applied against the blade to simultaneously form a substantial number of indentations in the thread form ridge.
Thread rolling dies are commonly provided with a face having thread form ridges with a dwell section in which the thread form ridges extend parallel to the back of the die. In addition, the face of the die may have a curved or tapered roll off section where the thread form ridges slope toward the back of the die to permit a blank to gradually lose contact with the die without marring the finished product. In order to prevent the indentations and/or projections formed in the flank of an external thread convolution from being marred as the finished bolt rolls off the dies, the indentations and/or projections in thread formed ridges in the roll off section should have the same configuration as indentations and/or projections formed in the dwell section of the thread form ridges.